1. Field of the Invention
The invention is related to the field of flow meters, and in particular, to Coriolis flow meters.
2. Description of the Prior Art
Mass flow rate is measured in a Coriolis flow meter by vibrating a fluid-carrying tube(s) in a sinusoidal motion and measuring the time delay (or phase angle) between the vibration response at two or more locations on the tube(s). For practical situations the time delay varies linearly with mass flow rate, however, the time delay is generally not zero at zero mass flow. There is usually a zero-flow delay or offset caused by a number of factors such as non-proportional damping, residual flexibility response, electromagnetic crosstalk, or phase delay in instrument electronics.
This zero-flow offset is typically corrected for by measuring the zero-flow offset at the zero-flow condition and subtracting the measured offset from subsequent measurements made during flow. This would be sufficient to correct for the zero-flow offset problem if the zero-flow offset remained constant. Unfortunately, the zero-flow offset can be affected by small changes in the ambient environment (such as temperature) or to changes in the piping system through which the material is flowing. The changes in the zero-flow offset will cause errors in the measured flow rates. During normal operations, there may be long periods of time between no-flow conditions. The Coriolis flow meter can be calibrated by zeroing the meter only during these no-flow conditions. The changes in the zero-offset over time may cause significant errors in the measured flow.
Therefore there is a need for a system and method for calibrating the zero-flow offset during flow.